Multiple-stage rotary drill



F. L. 0. WADSWORTH.

MULTIPLE STAGE ROTARY DHILL.

APPLICATION FILED OCT, 27. I919. LSQQfifiL 4 SHEETSSHEET I.

F. L. 0. WADSWORTH.

MULTIPLE STAGE ROTARY DRILL.

APPLICATION FILED 00127, 1919.

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Patented Dam 13, 1921.

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MULTIPLE STAGE ROTARY DRILL.

APPLICATION FILED OCT. 21, 1919.

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MULTIPLE STAGE ROTARY DRILL.

Patented Dem 113 4 SHEETSSHEET 4.

FLQWABSWORTH, anuewtoz 5&1, HIS aflo zmegym R 528m llmmlliulll APPLICATION FILED OCT. 27, I919.

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FRANK L. O. WADSWORTH, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO HUGHES TOOL COMPANY, OF HOUSTON, TEXAS, A CORPORATION OF TEXAS.

MULTIPLE-STAGE R0 TARY DRILL.

Application filed. October 27, 1919. Serial No. 333,506.

To (/71 lclmm if may concern Be it known that I. FRANK L. 0. Laoswoman a citizen of the l nited States, residing at. Pittsburgh; Allegheny county, Pennsylvania. have invented a certain new and useful Improvement in Multiple-Stage Rotary Drills. of which the following is a full, clear. and exact description, such as will enable others skilled in the art to which it appertains to make and use the same.

My invention relates to improvements in rotary boring drills for use in drilling wells or mines for water, oil, gas, etc., in earth,

rock, or similar formations. It has particular application to drills of the roller bit type, wherein the cutting action is performed by revoluble cutters designed to act upon the material being cut as the drill rotates on its longitudinal axis.

()ne object of my invention is to provide a drill ot' the character described which will act to engage the material being drilled in several stages. there being a forward pilot drill and separate sets of cutters behind the said pilot drill for the purpose ofenlarging the hole cut by the pilot drill to the desired size.

Another object is to construct a drill of the character described which will act to drill a hole in a true direct line thereby avoiding the difficulties experienced through drilling a crooked hole.

Another object is to provide a drill of the character described which will make it possible to combine varying structures of rotary cutters for the drilling operation thereby providing a tool which will best act to disintegrate the material at the bottom and sides of the hole in the manner desired.

Another object is to provide a drill of such structure that the danger of balling up the cutters will be greatly diminished due to the fact that the cutting action is better regulated, and also because the disintegration of the cutaway material, and its subsequent flushing away in suspension by streams of water, is effected at different elevations. instead of being confined to the bottom of the bore cavity.

Another object is to so form a drill as to obtain a compound tool, wherein the cutters of the first stage or pilot drill. may be used separately when desired to drill a hole of small size. Other objects and advantages of Patented Dec. 13, 1921.

my invention will moreclearly appear in the detailed description which follows Referring to the drawings forming a part of this specification wherein like numerals are used as far as possible to designate like parts throughout the several views. Figure 1 is a side elevation of one embodiment of my improved drill; Fig. 2 is a similar view taken at right angles to that shown in Fig. 1. one-half of the drill being shown in central longitudinal section; Fig. 3 is a bottom plan view, partly in section on the line 3-3 of Fig. 2; through the upper end of the pilot drill disclosed in Fig. 2, showing how the same may be used separately from the upper head; Fig. 5 is a side elevation of another embodiment of my invention; Fig. 6 is a View similar to Fig. 2, illustrating this embodiment; Fig. 7 is a transverse sectional view of the same taken on the line 7-7 of Fig. 6; Fig. 8 is a view similar to Fig. 4, showing the means of attaching the lower drill head to the drill stem: Fig. 9 is a side elevation of a still further embodiment of my invention;

Fig. 10 is a view taken at right angles to the.

ditl'erent embodiment of my invention; Fig.-

14 is a View at right angles to that shown in Fig. 13, part of the bit being shown in central longitudinal section; Fig. 15 is a bottom plan view thereof; Fig. 16 is a transverse section taken on the line 1616 of Fig. 14; and Fig. 17 is a view similar to that of Fig. 3 illustrating the manner in which the cutters therein shown may be mounted in offset axial relation to each other- In carrying out my invention I construct a rotary drill wherein there will be one set of cutters, placed in advance of the main head of the drill, and adapted to drill a pilot hole of relatively small size and a separate set of cutting members. placed behind the first set and adapted to enlarge the pilot bore which is formed by the advancecutters. Although I have disclosed in Figs. 1 to 16 inclusive, but two sets of cutters adapted to Fig. 4 is a longitudinal section' stage drill composed of three or more sets of cutting elements.

In the embodiment shown in Fig. 1, T have formed the head 21 of cylindrical shape, having the lower end thereof beveled on two opposite sides, each of the flat faces thus formed having thereon an integral cutter pin 22, upon which is mounted a disk-shaped cutter 23. The head 21 in this embodiment is adapted to fit slidably within the cylindrical recess 24 in the upper member 25 of the bit. This upper section 25 is also cylindrical in shape, having a reduced upper end 26 threaded interiorly for attachment to the drill stem 27. Two opposite side cutters 28 are supported upon the section 25, the said cutters being mounted upon opposite ends of a shaft 29, which extends diametrically through the section 25 and through a slot 38 in the upper portion of the head 21 of the pilot bit. The cutters 23 and 28 of the two stage sections are similar in structure, each being disk-shaped in form and provided with cutting teeth 30 upon the periphery thereof, and being recessed on the outer-face,as shown at 31-to provide a sharp cutting edge at the point where the outer face of the disk contacts with the sides of the hole. The cutter shaft 29 has, at one end thereof, a head 32 adapted to fit within a recess in the side of the head 25, the opposite end being reduced in diameter and threaded at 33 into the opposite side of the said head. Each end of the shaft is provided with a frusto-conical.

bearin 34, of somewhat smaller diameter than t e said shaft, and carries thereon a split bushing 35, which is engaged and held in place by the hub of the solid cutting member 28. in outer retaining washer 36, held in position by a set screw 37, serves to retain the cutter and its bushing in place on the said hearing. The cutters 23 on the lower end of the head are mounted on their bearings in the same way as the side cutters and no detailed description of the same will be necessary.

In order that the pressure upon the cutters in this embodiment of my invention may be varied automatically, according to the hardness of the material encountered by the upper and lower sets of drill members, I have so'constructed the head of the drill that the lower head 21 may have a sliding movement within the recess 24 in the head of the upper section. To secure this effect. I have made the central opening or slot 38 in the head 21 of the lower sectionthrough which the shaft 29 of the upper cutter is adapted to pass,of" somewhat elongated shape. The upper portion of the head 21 is also provided with a cylindrical recess 39, in the lower portion of which a helical spring 40 is placed. This spring bears at its lower end upon a packing washer 41 in the lower end of the recess 39 and at its upper end upon the cutter shaft 29. When the drill is operating in the hole the weight of the head and the superimposed drill stem will be supported partly upon the cutters 28 and partly upon the cutter 23. If a formation of unequal hardness is encountered by either of the sets of cutters, the pressure on the cutting edges thereof will be automatically increased on the harder and more resistant formation by the resilient contraction or expansion of the spring 40. This will serve to relieve any sudden shock or vibration due to the action of the cutters upon the harder material; and will further serve to vary and adjust the cutting action according to the resistance that is encountered.

The material that is cut away and disintegrated by the action of the revolving cutters is washed away from the cutters, and carried back upward to the surface of the ground in suspension, by streams of water pumped dowhwardly through the hollow drill stem 27 and through channels in the heads 21 and 25 to the cutting elements. The upper cutters are fed with water through channels 42 leading from the upper end of the bit in an inclined direction. so that the water will be projected upon the upper edges of the said cutters. The. lower cutters 23 are flushed by water conducted through channels 43,shown most clearly in Fig. 3,which lead from the upper end of the bit downwardly through the upper section 25 and issue from the lower shoulder thereof, so that the water will be discharged at a point between the lower cutters 23 and will act to flush away the material from the bottom of the hole. The water in the hole is prevented from finding entrance between the sliding sections 21 and 25 by means of a packing washer 44 fitting within an annular recess on the interior lower face of the recess 24 and forming a water-tight fit with the lower head 21 of the pilot bit.

Lubricating fluid is supplied to the bearings of the cutters through a central channel 45 in the upper head of this drill, the channel 45 being closed during operation by a threaded plug 46 in the upper end thereof. Lubricant is poured through the channel 45 into the recess 39 in the upper end of the lower head 21 and fills this central chamber. ings 34 through means of laterally branching ducts 47 in the shaft 29, said ducts leading from a point midway of said shaft outwardly to the bearings. Lubricant is supplied from the lower end of the chamber 39 through branching ducts 48 to the bearings of the cutters 23 in the same manner that it is supplied to the bearings of the cutters 28.

In order that the lower pilot bit 21 may be used alone without the upper head 25, T have threaded the upper end of this sec- It is conducted to the beara tion, as shown at 49, for attachment to a drill collar. When the head 21 is thus used alone a special drill collar 50,--shown in Fig. 4is used in attaching the head to the drill stem 27. This drill collar has a downwardly extending sleeve 51 adapted to close the opening 38 in the side of the head, thus preventing the entrance of rit or other foreign substance to the interior of the head. In order that the cutters 23 may be flushed with the water entering the recess 39 in the head of the bit, I provide laterally branching channels in the lower end of said recess, these channels acting to project the water upon the interior upper faces of the said cutters. It will be noted, by reference to Fig. 2, that these channels 52 are ordinarily closed by the packing washer 41, when this section is used in conjunction with the head 25 in a multiple stage bit, but this washer is removed when the lower head 21 is used alone.

Lubricant for the cutters 23,-when the head 21 is used separately,-is contained in a separate cylindrical container or cup 53, having a threaded nipple 54: on the lower end thereof for attachment in the lower end of the recess 39. This lubricant container may have an upper threaded plug 55 closing the opening through which the lubricant is poured into the said container. \Vhen the head 21 is thus mounted, it is obvious that it will be adapted to function in the same manner as the ordinary disk bit and may be so used when desired.

in the embodiment shown in Figs. 5, 6, 7 and 8, the construction is very similar to that shown in the embodiment first de-- scribed. The head 21 of this modification is adapted to reciprocate slightly within the upper head 25, the central opening 38 for the cross cutter shaft 29 being elongated vertically to allow for said reciprocation. The vertical movement of the head 21 within the upper head 25 is controlled by the action of the spiral spring 40". which in this embodiment is placed in the recess 39 in the upper end of the interior head 21, the said recess extending. downwardly to a oint adjacent the slot 38*. The spring 40 ears at its upper end against theupper end of the head 25*, and at its lower end upon the packing washer 41 which, except for a small central aperture-is adapted normally to close the lower end of the recess 39* in which the spring is housed. The cutters upon the pilot bit 21 are conical in shape and are of the construction disclosed in patent to Hughes No. 930,7 59 issued August 10th, 1909, as a preferred form of cutters for working in hard rock formation. These cutters 23 are mounted upon shafts 56 integral with the side sections of the head 21 the said head being split longitudinally on the line 57. The two sections of the head are adapted to be held in registered position by means of a transversely extending bolt 58 retained in place by the nut 59. The cutters 23 are mounted upon a removable bearing 60 adapted for threaded attachment to the shaft 56, the cutters being held in place on said bearing by means of locking washers 61.

The side cutters 28 on the upper head 25 are substantially identical in structure and mounting to those previously illustrated in Figs. 1 to 3 inclusive, and the numerals corresponding to those used in Figs. 1 to 3 are applied to corresponding parts in these views in such manner that no further description thereof is considered necessary. I

The manner in which the flushing water is conducted to the cutters through the passage ways 42 and 43 is also practically identical with that shown in the previous embodiment. and therefore this feature also needs no further description.

Placing the spring 40 above the shaft 29 instead of below the same, does not change the action thereof and in practice, such a positioning of the spring may be preferred because of the more convenient method of inserting it in place. In this embodiment, the cutters on the pilot bit 21 will be forced resiliently against the bottom of the hole, but it will also be noted that when the pilot bit meets with heavy resistance the head 25 will be supported resiliently upon the lower head by the action of the intervening sprung 40 thus producing the same equalizing effect previously described.

The means of supplying lubricant to the cutters in this embodiment is also similar to that disclosed in the previous embodiment with the exception that two separate ducts 48 are necessary to supply oil to the lower cutters 23 because of the fact that the head of the pilot bit is split or longitudinally divided in the manner described.

Fig. 8 illustrates how the pilot'bitsection of this construction may be used sep' arately by employing a drill collar 50 intc which the upper end of the head 21 is threaded ;--the said collar extending down wardly as shown at 51 to close the lateral slots 38 that are provided to receive the cross shaft of the cutters on the upper head. The lubricant container 53 in this modification. has a downwardly extending tube 51 adapted to project through the lower end of the chamber 39 and to be threaded into the head 21 at the lower face of the slot 38 as shown. lVater passages 52 normally closed by the packing washer 41, are provided on each side of the head for carrying the flushing water from the chamber 39 to the opening between the two cutters as shown in Figs. 6 and '2'.

This form of bit is adapted to function in the same manner as the embodiment previously described, the change in structure not affecting the operation thereof. The form of the cutters, however, adapts this drill for operation in hard formation, such as rock, the lower cone cutters thereof not being especially adapted for operation in soft formation. The action of the drill is otherwise substantially identical with the embodiment first described.

The modified form of cutting drill disclosed in Figs. 9 to 12 inclusive is also similar in general structure and operation to the two forms previously described, the two sections constituting the upper and lower head in this embodiment. however, not being resiliently connected. Both stages of the hole being drilled are cut out with conical or frusto-conical shaped cutters adapted to roll upon the bottom of the hole and to cut away and disintegrate the material by the chisel strokes of the cutter teeth upon the bottom of the excavation. The cutters of this bit are adapted especially for drilling hard formations but are not so well suited for operation in soft formations. The lower head 21 has cone shaped cutters 23" which are substantially the same in structure, and which are adapted to operate in the same manner as those illustrated in Fig. 6. The head 21 is divided longitudinally on the line 57 and the parts are retained in registered position by the transverse bolts 58", 58". The upper end of the head 21 is provided with a central channel or lubricant container 39" which communicates with a lower conical-shaped chamber 62, that is adapted to hold a considerable supply of lubricating fluid.

The upper head 25 is tubular in shape and is adapted'to fit closely over the upper end of the head :21 of the pilot bit section. The cutters Q8 o f this head are mounted upon inclined shafts 29 which are threaded at their inner ends into the base of the inner head, thereby joining the outer and inner heads against relative movement. The cutters 28 are frusto-conical in shape and, because of the inclined position of shafts 29", present the cutting edge 80 in approximately horizontal position for contact witl the bottom of the hole being dug.

The compound head formed by the two sections 21 and 25 is further retained in registered position by transverse bolts or pins 63, four in number, two of these pins being positioned toward the upper end of the head 21 and the other two at an intermediate point between the ends thereof. The head of the compound drill thus assembled is secured to the drill stem 27 by threading the upper end 26 of the outer section 25 for attachment thereto. This upper threaded shank of the bit is reinforced for greater strength by an outer ring adapted to be shrunk in position over the upper shank of the said bit.

The lubricant is contained within the central channel 39 and the chamber 62 as previously described; and an auxiliary lubricant chamber, 64, may also be formed in the outer section 25 of the head and connected to the channel 39 by means of the lateral passage 66. The cutter shafts :29 are bored axially to provide oil ducts 47 which feed the oil to the outer surfaces of said shafts to lubricate the bearingsurfaces for said cutters; and the bearings of the lower cutters 23 are supplied with oil through the passage ways 48*.

Flushing water for the upper cutters is furnished through channels 42 which lead directly to the slots or housings in which the cutters 28 are mounted. The flushing water is supplied to the lower cone cutters 23? through channels 52 which lead from the upper end of the head 21 directly downward along the line of division 57', and open into the upper ends of beveled recesses 67 on the side faces of the bit at points between the two lower cutters.

This embodiment of my invention acts to drill a forward pilot hole with the cutters 23 and to increase the diameter thereof by the cutters 28 in the same manner as in the previous embodiments. This structure will have the same advantagesin being able to drill a straighter hole, and to better maintain the gage of the hole-as are possessed by the previously described forms. It does not, however, have the advantage of an automatically equalized cutting action which is obtained by the interposition of an equalizer spring between the two sections of the drill head.

In the embodiment disclosed in Figs. 13 to 16, inclusive, I have used the equalizer spring between the two heads of my multiple stage drill; and have also shown different forms of cutting disks by which the drilling operation is performed. The lower pilot drill 21 is provided, in this embodiment, with disk cutters somewhat similar in structure to those illustrated in Figs. 1 to 3 inclusive; but the cutters 23" are mounted in slots 68 cut in the base of the head. These cutters are provided with spirally formed teeth 30 and have an outer annular groove or recess 31 around the margin of the outer face of the cutter, as in the embodiment first described. These cutters are mounted opposite each other upon a common shaft 29, supported at each end and at the center of the head. This shaft is retained against displacement by a transversely extending locking pin 69, of ordinary construction, in the central support. Antifriction washers 70 are provided on each side of these cutters; the said washers being mounted in recesses in the two faces move and disintegrate the material.

the disk cutters 23.

The upper head 25 is cylindrical in shape and recessed centrally to receive the upper end of the head 21; and an equalizer spring 40 similar to that shown in Fig. 6 .a; interposed between the adjacent ends of the two heads. A cross shaft 73 extending diametrically through the outer and inner heads prevents any accidental separation of the two drill sections,-an elongated slot 38 being provided in the head 21 in order to permit the said sections to move long1tu dinally with respect to each other under the action of the equalizing spring 40.

Cutters 28 are mounted on the lower end of the head 25, the said cutters being diskshaped and arranged to rotate on axes that are approximately parallel to the axlsof revolution of the drill stem. These cutting disks are preferably made integral with the upwardly extending shafts 74, 74 and each of said shafts is provided with an outwardly extending flange at the upper end thereof; thus providing an annular space between the upper and lower ends for an annular bushing 7 6 within which the cutter-shaft 74 is adapted to rotate. The cutter-shafts 74, 7 4 are housed in a slightly inclined position within lateral bosses 77 upon op osite sides of the head 25. Locking pins 8are provided on the outer faces of these bosses, the said pins being adapted to lock the bushings 76, 7 6 against rotation within the head and also to prevent removal of the shafts and bushings from their housings. As shown particularl in Fig. 13, the cutters 28 are inclined slightly forward so that the advancing edges thereof will dig into the bottom of the hole to shear away the material therefrom as the drill revolves. The outer peripheries of the cutters are preferably toothed as shown at 30, these teeth bearing on their outer faces upon the side of the hole so as to produce a rotation of the cutter as the drill revolves, and also maintain the gage of the bore as the drilling proceeds. It will be seen then that the forward cutting edge in contact with the bottom of the hole will have a shearing, as well as a scraping action, thus serving more efficiently to re This type of cutter is more fully disclosed in my co-pending application Serial No. 215,582 which has become Patent No. 1,338,301, issued April 27, 1920.

Lubricant is supplied to the bearings oi}.

the cutters 28 through channels or grooves 47 which lead from the lubricant chamber 39; and other lubricating ducts 48 conduct the lubricant downwardly through the lower head 21 to cooperating passages in the shafts 29 to the bearings of the lower cutters 23.

ater is supplied for the flushing away of the disintegrated material from the side cutters 28 through channels 42 leading downwardly from the end of the drill stem 27 to the lower face of the head 25 on which the cutters are mounted. The water is thus projected directly upon the inner edges of the cutters 28. As shown particularly in Figs. 14, and 16, laterally branching channels 57 lead from the channels 42 downwardly through the head 21 to the slots in which the cutters 23 are mounted-thereby serving to wash those cuttersv clear of disintegrated material and to carry the same upward around the head of the bit to the surface of the ground. This structure of bit is adapted for use in either soft or hard formation and is especially efficient in strata of varying degrees of hardness.

The cutter elements of the various illustrative embodiments shown and described in this specification may be provided with any approved form of cutting surface and I do not wish to confine myself to any particular character of cutting periphery. The cutters shown in Figs. 1 to 12 inclusive are mounted in diametrically opposite relation to each other; but my invention is not limited to that arrangement but may be equally well embodied in other constructions common to the art without departing from the spirit of my invention.

The construction and mode of operation of the multiple stage drills hereinbefore described present certain marked advantages over those forms of rotary bit structures in which the cutters serve to drill the hole in one stage and by the action of one set of cutters only. The combination of an advance set of relative small pilot cutters, with a following set or sets of enlarging cutters spaced behind the former, results in a bit construction which is not liable to be deflected from a straight course in passing from one strata of material to another of the other set an will thus tend to prevent the deflection of the bit from a straight line, thereby avoid g the danger of a crooked rare, the gage of the finished nes maintained by the upper set of cutte 1:; and these eutters'in foliow= ing behind piiot cutters are not sub jected to ch severe cutting duty and are liabie become quiet: dulled. This material'cut away by the upper or rearward cutters will fall downward into the lower end of the bore cavity and will be disintegrated by the pilot cutters in the bottom of the hole. The pilot cutters may therefore be used until they almost'entirely lose their effectiveness in removing the material from the end of the bore without any danger of losing the gage of the hole. or without sensibly diminishing the speed of the drilling operation. The upper side cutters only need to be replaced at long intervals. -This will reduce the number of sizes of cutters to be carried in stock in drilling, since only the upper cutters need be changed to vary the size of the hole within somewhat wide limits; it being obvious, that the upper cutters may be of large or small dimensions as compared to the forward pilot cutters, and that the size of the upper cutters is the determining factor in varying the size of the hole that is produced.

This type of bit construction will also enable one to combine cutting elements of different forms-such as cone cutters and disk cuttersand to mount these cutters in different positions relative to each other in order that the particular formation being drilled may be operated upon to the greatest advantage and in such manner as to meet widely varying field conditions.

The construction of a bit in separate stage sections in the manner described, will also be of advantage because of the increased rapidity and better regulation of the cutting action; and because the disintegration of the cut away material and its mixture with fiushing streams of water is effected at different levels instead of being confined to the very bottom of the bore cavity. A considerable part of the material cut away by the upper set of cutters will be carried upwardly, away from the drill head without having to be disintegrated by the pilot cutters at the forward end of the hole. I

By using the equalizer spring described in certain of the embodiments of my invention, the pressure upon the cutting elements may be better distributed and equalized so that excessive pressure upon any of the cutters is avoided and the consequent wear or injury of the same is thereby eliminated.

Having thus described my invention, the objects and advantages of which will now be apparent without further description, what I claim as new and desire to protect by Letters Patent is:

1. A multiple stage rotary earth boring drill comprising a two part head, one part of which is slidable resiliently within the other, roller cutters on the lower part and opposite disk cutters on the upper part arrangedto drill the hole outside the bore cut by the preceding cutters.

2. A multiple stage rotary drill comprising in combination a pilot bit, a transversely slotted upper shank thereon, a cylindrical head telescoping freely over the upper end of said shank, cutters on opposite sides of said pilot bit, a cutter shaft extending through said head and said slotted shank, and cutters thereon adapted to cut the hole outside the bore cut by said pilot bit.

3. A multiple stage rotary drill comprising in combination, a pilot bit having a head with roller cutters thereon, a second sleeveshaped head adapted to telescope over and be slidable freely'on said first named head, cutters on opposite sides of said second head, means to connect said heads together and to limit the movement of one relative to the other.

4. A multiple stage drill comprising in combination a pilot bit with a cylindrical upper shank a second sleeve-shaped bit mounted on t e said upper shank, cutters on both said bits, a shaft for the cutters of said second bit passing through said shank and said sleeve-shaped bit and acting to secure them slidably together, alubricant container in said pilot bit and means to feed lubricant to the cutters of both bits.

5. A multiple stage drill comprising in combination two separate heads, one of said heads slidable within the other, cutters on both said heads and resilient means to relieve the pressure upon said cutters.

6. A multiple stage rotary drill comprising in combination, a pilot drill, a second drill adapted to cut a hole of larger diameter adapted to fit slidably upon the upper end of said pilot drill, cutters on each of said drills and resilient means to relieve the inequalities of pressure upon said cutters.

7. A multiple stage rotary, drill comprising in combination, a pilot hit, an upper shank thereon, a second bit above said pilot bit and adapted to fit slidably upon said upper shank, a cross shaft on said second bit reciprocable within a slot in said uppershank and serving to retain said bits together, and resilient means to cushion shocks on said pilot cutters.

8. A multiple stage rotar drill comprising, in combination, a tubular head, rotary cutters thereon, a pilot bit reciprocable in said head and a pressure means adapted to force said head and said bit resiliently apart.

9. A multiple stage rotary drill comprising in combination, a tubular head, a pilot bit adapted to reciprocate in said head, rotatable cutters on said bit and said head, and a spring between said head and said bit adapted to relieve shocks upon the cutters of said pilot bit.

10. A. multiple stage rotary drill comprising in combination, a tubular head, a pilot bit adapted to reciprocate in said head, means to limit said reciprocation, rotatable cutters on said bit and said head and means to cushion the pressure upon the cutters on said bit.

11. A multiple stage rotary drill comprising in combination a tubular head. a pilot bit slidahle within said head. a diametrical cutter shaft in said head. said pilot bit having a slot therein to receive said shaft and cutters on said head and said hit.

12. A multiple stage rotary drill comprising in combination. a tubular head. a pilot bit having a cylindri 'al shank slidable withinsaid head. a spring between said head and said pilot bit acting to force said bit away from said head. means to limit the downward movement of said pilot bit, and cutters on said head and said bit. the cutters on said head being adapted to enlarge the hole drilled by said pilot bit.

13. A compound rotary drill comprising a pilot hit. an upper slotted shank on said bit. a tubular head fitting over said shank, means to retain said shank slidahly in said head. resilient means between said head and said shank and cutters on said head and said bit, said bit being adapted for use separately from said head. i

14. A compound rotary drill comprising a tubular head. a pilot bit with a tubular upper shank reciprocable in' said outer tubular head. a cutter shaft arranged diametrically of said head and said shank, cutters on said bit and said shaft and resilient means hearing on said bit and said head for the purpose described.

15. A compound rotary drill comprising a Forward pilot bit having a head. a reduced upper shank thereon. a second head slidahle freely over said shank. a recess on the inte rior of one of said heads. a spring in said recess. rolling cutterson both said heads. and oil ducts leading from said recess t0 the said cutters.

16. A compound rotary drill comprising a pilot bit, a second bit telescoping over the upper end of said pilot bit, cutters on said pilot bit. a shaft extending, transversely through both said bits. and cutters rotatable on the outer ends of said shat't. adapted to cut the hole outside the bore of said pilot bit. said shaft acting to secure said bits together and limit the vertical movement of one relative to the other.

17. In a multiple stage drill a pilot bit. cutters thereon, a second bit having a head telescoping over said pilot hit. cutters on said second bit of larger diameter than said pilot cutters. and means on which said second cutters are mounted adapted to assist in securing said bits together. Y

I In testimony whereof. I hereunto affix my signature this the 25th day of October A. D.

f, FRANK L. O. WADSWORTH. 

